This invention relates to a device for measuring the fluid density of a two-phase mixture flowing through a tube. With the increased emphasis on safety, designers of pressurized water nuclear reactors are seeking to develop instrumentation capable of accurately measuring both single-phase and two-phase flow. Measurement of two-phase flow is difficult because of rapidly changing fluid densities and flow regimes. This measurement is especially difficult in the harsh environment of a nuclear reactor system.
An instrument presently used to measure two-phase flow in nuclear reactors is a drag disk turbine transducer (DDT). The DDT consists of a spring mounted drag disk and a turbine rotor in series within a common shroud. A variable reluctance transducer senses drag disk deflection which is proportional to the fluid density multiplied by the fluid velocity squared. The rotor speed, which is directly proportional to fluid velocity is sensed by an eddy current transducer. Recorded data from the variable reluctance and eddy current transducers are correlated to yield a mass flow rate versus time which is the fluid density of the two-phase mixture or two-phase flow.
The DDT is designed to measure flow in both forward and reverse directions. During forward flow, the drag disk shadows the rotor, while during reverse flow the rotor shadows the drag disk. Because the drag disk and rotor are separated axially and all of the two-phase mixture that contacts the rotor does not contact the drag disk, there is concern about data correlation over all encountered flow regimes.